Conventional techniques for dissipating heat of an electricity storage element are known. Patent Document 1 (JP 2010-211963A) discloses a battery module in which positive electrode terminals and negative electrode terminals of a plurality of single cells are electrically connected via busbars and that is accommodated in a packing case. Heat dissipation fins are provided on the top of the packing case. A coolant is placed in the lower portion of the packing case, and the coolant absorbed by an absorption sheet is evaporated and condensed, so that heat of the battery is dissipated from the heat dissipation fins to the outside.